1. Field:
This invention relates to an improved flow control device and in particular for a device for regulating the flow of liquid passing through flexible tubing which permits very fine adjustment to changes in rates of flow.
2. Prior Art:
A great many flow control devices have been disclosed, particularly of the types which have means for compressing the walls of flexible tubing. Some utilize the action of a cammed surface against the tubing to achieve variable compression as a means for varying the flow rate. Typical of such devices are shown in U.S. Pat. Nos. 3,289,999; 3,299,904; 3,477,454; 3,625,472; 3,805,830; 3,813,077 and 4,034,773. Another type which employs the action of a screw is shown in U.S. Pat. Nos. 3,477,686 and 3,584,830. Still another type which utilizes a hinged lever whose free end is urged against tubing is illustrated in U.S. Pat. Nos. 3,497,175; 3,612,474 and 4,091,815. The most common flow control devices in use currently in the medical field are those which are termed roller clamps similar to those shown in U.S. Pat. Nos. 3,099,429; 3,685,787 and 3,802,463.
One of the chief deficiencies of these aforementioned devices resides in their inability to allow small differences in the rate of flow to be effected. For example, in roller clamps used on parenteral solution administration sets, the roller is in direct contact with the tubing and the distance a roller is moved on the tubing between a setting for delivery of several hundred milliliters of solution to a setting for just a few milliliters per hour is only fractions of an inch. This makes it extremely difficult if nigh impossible for a nurse to change an established flow rate to a rate which is only slightly greater or slightly less. This is a source of constant annoyance and often leads to a solution being delivered too rapidly or too slowly which can be detrimental to the patient. Another problem associated with clamped tubing, particularly with polyvinyl chloride tubing, is the change in flow rate from a preset rate because of the property of "cold flow" associated with such tubing when under compression. Still another deficiency of roller clamps is the difficulty in establishing a particular flow rate. The axle of the roller rides in the grooves on the side walls and normally the grooves are made larger than the axle so the roller will move easily. However, when an operator pushes the roller with his thumb to set the roller at a particular position, as he releases his thumb, the roller is forced upwardly very slightly by the compressed tubing so that a greater flow results over what existed when his thumb was on the roller.
Another problem with roller clamps is that the roller can occassionally become dislodged from a preset position by relatively gentle tugs on the tubing from inadvertent movements of the patient. This could open up the tubing orifice and produce too rapid an infusion which could be extremely detrimental.
These and other deficiencies are eliminated with an improved flow control device of the present invention as herein disclosed.